Optical element and imaging device

ABSTRACT

An optical element includes a first liquid; a second liquid that is immiscible with the first liquid and that has polarity or electrical conductivity; a first substrate portion; a second substrate portion; a sidewall portion; a second electrode disposed on one of the second substrate portion and the sidewall portion; and an accommodating portion constituted by the first substrate portion, the second substrate portion, and the sidewall portion and sealing the first liquid and the second liquid therein. The optical element further includes a first film disposed on the first substrate portion side of the accommodating portion and having high affinity with the first liquid, a second film disposed on the second substrate portion side of the accommodating portion and having high affinity with the second liquid, and a third film disposed at the center of the second film and having high affinity with the first liquid.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority to Japanese Priority PatentApplication JP 2008-249240 filed in the Japan Patent Office on Sep. 26,2008, the entire content of which is hereby incorporated by reference.

BACKGROUND

The present application relates to an optical element and an imagingdevice. More specifically, the present application relates to an opticalelement utilizing an electrowetting phenomenon and an imaging deviceincluding the same.

In imaging optical systems used in imaging devices such as a stillcamera and a video camera, it is necessary for such imaging opticalsystems to have functions of adjusting the focus and adjusting theamount of light, to realize natural defocusing, to make the distributionof the amount of light on an image surface to be uniform etc. Amongthese requirements, in general, the requirement for adjusting the amountof light is met by a mechanical aperture mechanism including a pluralityof movable blades.

However, such a mechanical aperture mechanism has the followingproblems: A mechanical driving unit for driving the movable blades isnecessary, and thus the size of the device increases. In addition, in asmall aperture state in which an opening of the aperture mechanism issmall, diffraction of a light beam occurs, thereby decreasing theresolution of an acquired image. Furthermore, a sound is generatedduring the operation of the aperture mechanism.

To solve the above problems in such a mechanical aperture mechanism,optical elements using an electrocapillarity (electrowetting phenomenon)have been proposed (refer to, for example, Japanese Unexamined PatentApplication Publication No. 2000-356792 (document '792)). FIG. 18 is aschematic view of an optical element disclosed in document '792. Anoptical element 100 described in document '792 is an optical elementconfigured to control the amount of light beam 30 passing through theelement (the amount of transmitted light).

The optical element 100 is configured so that a transparent substrate102 and a transparent cover plate 106 are liquid-tightly sealed on alower opening and an upper opening, respectively, of a cylindricalcontainer 105 by adhesion or the like. A transparent electrode 103, aninsulating layer 104, and a water-repellent film 111 are provided on theinner surface of the transparent substrate 102 in that order. Ahydrophilic film 113 is provided on the inner surface of the transparentcover plate 106. A rod-shaped electrode 125 is provided so as topenetrate through the container 105, and an end of the rod-shapedelectrode 125 is in contact with a first liquid 121. The first liquid121 and a second liquid 122 are hermetically sealed in a spaceconstituted by the hydrophilic film 113, the water-repellent film 111,and the inner wall of the container 105. The first liquid 121 is aliquid having electrical conductivity or polarity, and the second liquid122 is a liquid that is immiscible with the first liquid 121. Therefractive index of the first liquid 121 is substantially the same asthe refractive index of the second liquid 122, but the transmittance ofthe first liquid 121 is different from the transmittance of the secondliquid 122.

According to the optical element 100 described in document '792, avoltage is applied between the transparent electrode 103 and therod-shaped electrode 125, and thus the shape of the interface betweenthe two liquids is changed through the electrowetting phenomenon. As aresult, a part of the surface of the second liquid 122 on thehydrophilic film 113 side contacts the hydrophilic film 113 to form onthe hydrophilic film 113 an opening through which light can betransmitted (to form an optical path in the optical element 100). Inthis optical element 100, the size of the opening formed on thehydrophilic film 113 is changed by changing the voltage applied, thusadjusting the amount of light beam 30 passing through the opticalelement 100. That is, according to this optical element 100, the amountof light can be electrically controlled, and thus it is possible tosolve the shortcomings of the mechanical aperture mechanism describedabove.

SUMMARY

In the optical element using an electrowetting phenomenon, decentrationof an opening provided on the light-incident side readily occurs, andthe amount of decentration is also large. In such a case, a problem ofdecreasing the resolution occurs. To solve this problem, in document'792, the transparent electrode 103 is formed such that the shape of thetransparent electrode 103 is a concave shape when viewed from the liquidside. However, this structure causes a problem that it is difficult toreduce the thickness of the optical element 100. Furthermore, in theoptical element 100 described in document '792, since the transparentelectrode 103 is formed so as to have a concave shape viewed from theliquid side, the structure of the optical element 100 becomes complexand it is difficult to make the optical element 100 and to reduce thesize of the optical element 100.

In an optical element using an electrowetting phenomenon, it isdesirable to suppress decentration of an opening with a simplerstructure.

An optical element according to an embodiment includes a first liquidand a second liquid that is immiscible with the first liquid and thathas polarity or electrical conductivity. The optical element accordingto an embodiment further includes a first substrate portion, a secondsubstrate portion, a sidewall portion, a second electrode disposed onone of the second substrate portion and the sidewall portion, and anaccommodating portion constituted by the first substrate portion, thesecond substrate portion, and the sidewall portion and sealing the firstliquid and the second liquid therein. The first substrate portionincludes a first substrate having optical transparency, a firstelectrode disposed on a surface of the first substrate and havingoptical transparency, and an insulating film disposed on the firstelectrode and having optical transparency. Furthermore, the firstsubstrate portion includes a first film disposed on the insulating filmand having higher affinity with the first liquid than with the secondliquid and optical transparency. The second substrate portion includes asecond substrate having optical transparency, a second film disposed ona surface of the second substrate and having higher affinity with thesecond liquid than with the first liquid and optical transparency, and athird film disposed at the center of the second film and having higheraffinity with the first liquid than with the second liquid and opticaltransparency. The sidewall portion connects the first substrate portionto the second substrate portion so that the first film and the secondfilm face each other.

An imaging device according to an embodiment includes the opticalelement according to an embodiment, a power supply unit configured toapply a voltage between the first electrode and the second electrode ofthe optical element, a lens unit configured to focus incident light, andan imaging element on which the light is focused through the opticalelement and the lens unit.

In an embodiment, the third film having higher affinity with the firstliquid than with the second liquid is provided at the center of thesecond film of the second substrate portion. Therefore, in the casewhere no voltage is applied, the first liquid is fixed by being incontact with not only the first film of the first substrate portion butalso the third film of the second substrate portion. Accordingly, acontact area between the first liquid and a film on the second substrateportion side of the accommodating portion is formed on the third film orin an area centering on the third film.

In an embodiment, the third film having higher affinity with the firstliquid than with the second liquid is provided at the center of thesecond film of the second substrate portion. This structure can suppressa shift of the center of a contact area between the first liquid and afilm of the accommodating portion on the second substrate portion sidefrom the optical axis. That is, according to the embodiment,decentration of the contact area between the first liquid and the filmof the accommodating portion on the second substrate portion side can besuppressed with a simpler structure.

When the optical element according to an embodiment is applied to anaperture mechanism (iris) of an imaging device or the like, theabove-mentioned contact area functions as an opening through which lightis transmitted. Accordingly, in such a case, decentration of the openingcan be suppressed with a simpler structure.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic view of an imaging device according to a firstembodiment;

FIG. 2A is a schematic cross-sectional view of a liquid iris accordingto the first embodiment:

FIG. 2B is a top view of the liquid iris shown in FIG. 2A, viewed fromthe light-incident side;

FIG. 3A is a schematic cross-sectional view of a liquid iris in thestatic state;

FIG. 3B is a top view of the liquid iris shown in FIG. 3A in the staticstate, viewed from the light-incident side;

FIG. 4A is a schematic cross-sectional view of a liquid iris of acomparative example in the static state;

FIG. 4B is a top view of the liquid iris of the comparative exampleshown in FIG. 4A in the static state, viewed from the light-incidentside;

FIG. 5 is a flowchart showing a procedure for making the liquid iris ofthe first embodiment;

FIG. 6A is a view showing a state of a polar liquid before a voltage isapplied to the polar liquid;

FIG. 6B is a view showing a state of the polar liquid when a voltage isapplied to the polar liquid;

FIG. 7A is a schematic cross-sectional view of a liquid iris when avoltage is applied;

FIG. 7B is a top view of the liquid iris shown in FIG. 7A, viewed fromthe light-incident side when the voltage is applied;

FIG. 8 is a view showing the principle of an operation of the liquidiris;

FIG. 9A is a schematic cross-sectional view of the liquid iris when avoltage is applied;

FIG. 9B is a top view of the liquid iris shown in FIG. 9A, viewed fromthe light-incident side when the voltage is applied;

FIG. 10A is a schematic cross-sectional view of a liquid iris accordingto a second embodiment:

FIG. 10B is a top view of the liquid iris shown in FIG. 10A, viewed fromthe light-incident side;

FIG. 11 is a view showing a first electrode of the second embodiment;

FIG. 12 is a view showing the principle of a decentration control by thefirst electrode;

FIG. 13 is a view showing an example of the first electrode;

FIG. 14 is a view showing an example of the first electrode;

FIG. 15 is a view showing an example of the first electrode;

FIG. 16 is a view showing an example of the first electrode;

FIG. 17 is a view showing an example of the first electrode; and

FIG. 18 is a schematic cross-sectional view of an optical element in therelated art.

DETAILED DESCRIPTION

The present application will now be described with reference to thedrawings according to an embodiment. As described below, opticalelements according to embodiments will be described using an aperturemechanism (iris) used in an imaging device as an example. Note thatembodiments are not limited to examples described below.

First Embodiment Structure of Imaging Device

FIG. 1 shows an example of the schematic structure of an imaging deviceto which an aperture mechanism (hereinafter referred to as “liquidiris”) of this embodiment is applied. FIG. 1 shows an example of animaging device including a zoom mechanism. FIG. 1 mainly shows thestructure of an optical system of the imaging device, and the structuresof a portion configured to process an acquired image and a portionconfigured to perform a control process of the optical system areomitted. The embodiment can be applied also to an imaging device thatdoes not include a zoom mechanism.

An optical system of an imaging device 20 includes a first lens unit 1,a second lens unit 2, a liquid iris 10, a third lens unit 3, a fourthlens unit 4, a filter 5, and an imaging element 6. The first lens unit1, the second lens unit 2, the liquid iris 10, the third lens unit 3,the fourth lens unit 4, the filter 5, and the imaging element 6 arearranged in that order from the incident side of a light beam 30.

Among the first lens unit 1 to the fourth lens unit 4 for focusingincident light, the first lens unit 1 and the third lens unit 3 areattached so as to be fixed in a lens barrel (not shown). The second lensunit 2 is a lens unit for zooming and is attached to the lens barrel soas to move in a direction of an optical axis 7. The fourth lens unit 4is a lens unit for focusing and is attached so as to move in thedirection of the optical axis 7. The movement of the second lens unit 2(for zooming) and the fourth lens unit 4 (for focusing) in the directionof the optical axis 7 is controlled by a control unit (not shown) in theimaging device 20.

The liquid iris 10 (optical element) adjusts an opening diameter(aperture diameter) of the liquid iris 10 at the light-incident side byutilizing an electrowetting phenomenon, whereby adjusting the amount oflight beam 30 passing through the liquid iris 10. The opening diameter(aperture diameter) of the liquid iris 10 at the light-incident side isadjusted by changing the value of voltage applied to the liquid iris 10,and this adjustment is controlled by the control unit (not shown) in theimaging device 20. The specific structure and the operation of theliquid iris 10 will be described in detail below.

The filter 5 is constituted by an infrared cut filter, a low-passfilter, or the like. The imaging element 6 is constituted by, forexample, charge coupled devices (CCD) or complementary metal oxidesemiconductors (CMOS).

In the imaging device 20 of this embodiment, as shown in FIG. 1, thelight beam 30 incident from the first lens unit 1 side is focused on animaging surface 6 a of the imaging element 6 through the above-mentionedvarious optical elements. An image data acquired in the imaging element6 is subjected to a predetermined process by an image-processing unit(not shown) in the imaging device 20.

[Structure of Liquid Iris]

FIGS. 2A and 2B show the schematic structure of the liquid iris 10 ofthis embodiment. FIG. 2A is a schematic cross-sectional view of theliquid iris 10 when no voltage is applied (hereinafter, this state isalso referred to as “static state”), and FIG. 2B is a top view of theliquid iris 10 viewed from the light-incident side at that time.

The liquid iris 10 includes a first substrate portion 11, a secondsubstrate portion 21, and a sidewall portion 31 connecting the firstsubstrate portion 11 to the second substrate portion 21. A first liquid41 and a second liquid 42 are hermetically enclosed in an accommodatingchamber 40 (accommodating portion) constituted by the first substrateportion 11, the second substrate portion 21, and the sidewall portion31.

As the first liquid 41, a liquid that has an insulating property ornonpolarity, and that has optical transparency is used. Any liquidhaving such properties can be used as the first liquid 41. For example,silicone oil is used as the first liquid 41. There are various types ofcommercially available silicone oil having different specific gravitiesand refractive indices. Accordingly, when silicone oil is used as thefirst liquid 41, among various types of commercially available siliconeoil, silicone oil having substantially the same specific gravity andrefractive index as those of the second liquid 42 described below isselected and used as the first liquid 41.

On the other hand, as the second liquid 42, a liquid that is immisciblewith the first liquid 41, that has substantially the same specificgravity and refractive index as those of the first liquid 41, and thathas polarity or electrical conductivity is used. Any liquid having suchproperties can be used as the second liquid 42. For example, whensilicone oil is used as the first liquid 41, water (specific gravity: 1,refractive index: 1.333) can be used as the second liquid 42. In thiscase, instead of water, a mixed liquid of water and ethanol, a mixedliquid of water, ethanol, and ethylene glycol, a mixed liquid preparedby adding common salt to a mixed liquid of water and ethanol, or thelike can also be used. In this embodiment, in order to make opticaltransparency of the second liquid 42 lower than that of the first liquid41 (in order to decrease optical transparency of the second liquid 42),the second liquid 42 (e.g., water) is colored by mixing carbon black orthe like. A dye other than carbon black may be used as a colorant.

Furthermore, in order to make the specific gravity and the refractiveindex of the second liquid 42 to be closer to those of the first liquid41, for example, a liquid prepared by mixing ethanol, ethylene glycol,common salt etc. with water is used as the second liquid 42, and thespecific gravity and the refractive index of the second liquid 42 may becontrolled by adjusting the mixing ratio of these. By adjusting therefractive index of the second liquid 42 to be substantially the same asthe refractive index of the first liquid 41, refraction of light (lenseffect) at the interface between the first liquid 41 and the secondliquid 42 can be prevented or sufficiently decreased, thereby performingthe operation of an aperture of the liquid iris 10 more reliably.Furthermore, by adjusting the specific gravity of the second liquid 42to be substantially the same as the specific gravity of the first liquid41, a change in the shape of the interface between the first liquid 41and the second liquid 42 can be suppressed when the whole device isvibrated or tilted. Note that it is sufficient that the values of thespecific gravity and refractive index of the second liquid 42 are closeto those of the first liquid 41 to an extent that optical properties, avibration resistance property etc. of the device are within allowabletolerances of the device.

The first substrate portion 11 includes a first substrate 12, a firstelectrode 13 disposed on the first substrate 12, an insulating film 14disposed on the first electrode 13, and a first water-repellent film 15disposed on the insulating film 14.

The first substrate 12 is a square plate-shaped member composed of alight-transmissive material such as transparent glass and having athickness of, for example, about 0.2 to 0.3 mm. Alternatively, atransparent synthetic resin material may be used as the material of thefirst substrate 12. The first electrode 13 is a transparent electrodecomposed of indium tin oxide (ITO) or the like. The first electrode 13is connected to a terminal of a power supply 8 of the imaging device 20.The insulating film 14 is a dielectric film composed of polyvinylidenechloride, polyvinylidene fluoride, or the like.

The first water-repellent film 15 (first film) is a thin film(hydrophobic or lipophilic thin film) having higher affinity with thefirst liquid 41 (nonpolar liquid) than with the second liquid 42 (polarliquid). That is, the wettability of the first liquid 41 on the firstwater-repellent film 15 is larger than the wettability of the secondliquid 42 on the first water-repellent film 15. In this embodiment, afluorocarbon resin or the like is used as a material of the firstwater-repellent film 15. Any thin film having lipophilicity and opticaltransparency may be used as the first water-repellent film 15.

The second substrate portion 21 includes a second substrate 22, a secondelectrode 23 disposed on the second substrate 22, a hydrophilic film 24disposed on the second electrode 23, and a second water-repellent film25 disposed at the center of the hydrophilic film 24.

As in the first substrate 12, the second substrate 22 is a squareplate-shaped member composed of a light-transmissive material such astransparent glass and having a thickness of, for example, about 0.2 to0.3 mm. As in the first electrode 13, the second electrode 23 is atransparent electrode composed of ITO or the like. The second electrode23 is connected to another terminal of the power supply 8 of the imagingdevice 20.

The hydrophilic film 24 (second film) is a thin film having higheraffinity with the second liquid 42 (polar liquid) than with the firstliquid 41 (nonpolar liquid). That is, the wettability of the secondliquid 42 on the hydrophilic film 24 is larger than the wettability ofthe first liquid 41 on the hydrophilic film 24. In this embodiment, apolyvinyl alcohol resin, a polyacrylic acid resin, or the like is usedas a material of the hydrophilic film 24. Any thin film havinghydrophilicity and optical transparency may be used as the hydrophilicfilm 24.

As in the first water-repellent film 15, the second water-repellent film25 (third film) is a thin film (lipophilic thin film) having higheraffinity with the first liquid 41 (nonpolar liquid) than with the secondliquid 42 (polar liquid). In this embodiment, the same material as thefirst water-repellent film 15 is used as a material of the secondwater-repellent film 25. Note that the material constituting the secondwater-repellent film 25 may be the same as or different from thematerial constituting the first water-repellent film 15.

The surface of the second water-repellent film 25 at the accommodatingchamber 40 side is circular in shape (see FIG. 2B). The embodiment isnot limited thereto, and the surface of the second water-repellent film25 may have a shape other than a circular shape. However, as describedbelow, in this embodiment, an opening 50 that transmits light expandscentering on the second water-repellent film 25. In this case, theplanar shape of the opening 50 is preferably a circular shape inconsideration of the resolution. Therefore, in order to maintain theplanar shape of the opening 50 to be a circular shape, the surface ofthe second water-repellent film 25 is preferably circular in shape.

In this embodiment, since the second water-repellent film 25 havinghigher affinity with the first liquid 41 than with the second liquid 42is provided at the center of the hydrophilic film 24, as shown in FIG.2A, a part of the first liquid 41 contacts the second water-repellentfilm 25 even in the static state. As a result, as shown in FIG. 2B, theopening 50 is formed at the light-incident side even in the staticstare. Accordingly, in order to increase the range of a change in thediameter of the opening 50, the diameter of the opening 50 in the staticstate is preferably as small as possible. That is, the diameter of thesecond water-repellent film 25 is preferably as small as possible.

Furthermore, preferably, the thickness of the second water-repellentfilm 25 is substantially the same as the thickness of the hydrophilicfilm 24. Specifically, it is preferable that a surface of the secondwater-repellent film 25 on the accommodating chamber 40 side be flushwith a surface of the hydrophilic film 24 on the accommodating chamber40 side. The reason for this is as follows. If the thickness of thesecond water-repellent film 25 is different from the thickness of thehydrophilic film 24, and a difference in level is generated on thesurface at the accommodating chamber 40 side, optical properties arechanged by the portion including the difference in level and thus it isdifficult to obtain desired optical properties. Furthermore, from thestandpoint of the optical properties of the liquid iris 10, materials ofthe hydrophilic film 24 and the second water-repellent film 25 arepreferably selected so that the refractive index of the hydrophilic film24 is as close to the refractive index of the second water-repellentfilm 25 as possible. Note that it is sufficient that the values of thethickness and the refractive index of the hydrophilic film 24 are closeto those of the second water-repellent film 25 to an extent that opticalproperties of the device are within allowable tolerances of the device.

The sidewall portion 31 includes a cylindrical sidewall member 32 and ahydrophilic film 33 provided on the inner wall surface of the sidewallmember 32.

The sidewall member 32 is a cylindrical member composed of an insulatingmaterial (such as glass). In this embodiment, the sidewall member 32 hasan inner diameter of about 9 mm, an outer diameter of about 11 mm, and aheight of about 1 mm. The sidewall member 32 includes an inlet 32 a forinjecting the first liquid 41 and the second liquid 42 into the liquidiris 10. The inlet 32 a is sealed from the outside of the sidewallmember 32 using an adhesive member 34.

The hydrophilic film 33 (fourth film) is a thin film having higheraffinity with the second liquid 42 (polar liquid) than with the firstliquid 41 (nonpolar liquid). In this embodiment, as in the hydrophilicfilm 24 of the second substrate portion 21, a polyvinyl alcohol resin, apolyacrylic acid resin, or the like is used as a material of thehydrophilic film 33. Any thin film having hydrophilicity and opticaltransparency may be used as the hydrophilic film 33.

An alternating-current power supply is used as the power supply 8 (powersupply unit) of the imaging device 20 to which the first electrode 13and the second electrode 23 are connected. A direct-current power supplymay also be used as the power supply 8. However, in such a case, whenthe power supply is set to the off-state from a voltage-applied state,electrical charges are somewhat left on the insulating film 14.Accordingly, the speed of an operation for which the first liquid 41 isreturned to the original static state becomes somewhat lower than thecase where an alternating-current power supply is used. Therefore, analternating-current power supply is more preferably used as the powersupply 8.

[Principle of Suppression of Decentration]

A description will be made of the principle of suppressing decentrationof the opening 50 in the liquid iris 10 of this embodiment. In theliquid iris 10 of this embodiment, in the case where no voltage isapplied between the first electrode 13 and the second electrode 23 (inthe static state), the interface between the first liquid 41 and thesecond liquid 42 is in the state shown in FIG. 2A.

More specifically, the first water-repellent film 15 is provided overthe entire surface of the accommodating chamber 40 on the firstsubstrate portion 11 side, and thus the first liquid 41 having higherwettability on the first water-repellent film 15 spreads over andcontacts the first water-repellent film 15. In addition, the secondwater-repellent film 25 is provided at the center of the surface of theaccommodating chamber 40 on the second substrate portion 21 side.Accordingly, a part of the surface of the first liquid 41 on the secondsubstrate portion 21 side contacts the second water-repellent film 25.Specifically, in this embodiment, in the accommodating chamber 40, thefirst liquid 41 is fixed to the first water-repellent film 15 on thefirst substrate portion 11 side and the second water-repellent film 25on the second substrate portion 21 side.

On the other hand, the second liquid 42 is disposed so as to contact thehydrophilic film 24 provided on the second substrate portion 21 side ofthe accommodating chamber 40 and the hydrophilic film 33 provided on thesidewall portion 31 side thereof and to surround the first liquid 41.

The interface between the first liquid 41 and the second liquid 42 has aspherical shape. This shape is determined by the balance of the surfacetensions of the first liquid 41 and the second liquid 42, and theinterfacial tensions on the first water-repellent film 15. The firstliquid 41 spread on the first water-repellent film 15 close to thesidewall portion 31 as shown in FIG. 2A. However, since the hydrophilicfilm 33 is provided on the sidewall portion 31 side of the accommodatingchamber 40, the first liquid 41 does not contact the sidewall portion31.

As described above, a part of the first liquid 41 is fixed to the secondwater-repellent film 25 provided on the second substrate portion 21side. Since the second water-repellent film 25 is disposed at the centerof the hydrophilic film 24, the center of the second water-repellentfilm 25 is located at substantially the same position as the opticalaxis. Accordingly, the center position of a contact area between thefirst liquid 41 and the second water-repellent film 25, i.e., the centerposition of the opening 50 formed on the light-incident side (secondsubstrate portion 21 side) of the liquid iris 10 is substantiallydisposed on the optical axis, thus suppressing decentration.

As described above, in this embodiment, by utilizing not only theaffinity between the first water-repellent film 15 and the first liquid41 but also the affinity between the second water-repellent film 25 andthe first liquid 41, decentration of the first liquid 41, i.e.,decentration of the opening 50 is suppressed. More specifically, athree-dimensional control of decentration suppression can be performedin this embodiment. FIGS. 3A and 3B illustrate this feature.

FIG. 3A is a schematic cross-sectional view of the liquid iris 10 in thestatic state, and FIG. 3B is a top view of the liquid iris 10 in thestatic state viewed from the light-incident side. In FIG. 3A, a conceptof the three-dimensional control of decentration suppression of theliquid iris 10 of this embodiment is represented by the black dots.

For comparison, FIGS. 4A and 4B show a concept of decentrationsuppression in a liquid iris 90 (comparative example) that does notinclude the second water-repellent film 25. FIG. 4A is a schematiccross-sectional view of the liquid iris 90 of the comparative example inthe static state, and FIG. 4B is a top view of the liquid iris 90 of thecomparative example in the static state, viewed from the light-incidentside. In the comparative example, decentration is suppressed byutilizing only the affinity between the first water-repellent film 15and the first liquid 41, and thus a two-dimensional control ofdecentration suppression is performed (see black dots in FIG. 4A).Accordingly, in the liquid iris 90 of the comparative example, theeffect of suppressing decentration is smaller than that of the presentembodiment.

As described above, in this embodiment, the second water-repellent film25 having higher affinity with the first liquid 41 than with the secondliquid 42 is provided at the center of the hydrophilic film 24 on thelight-incident side of the liquid iris 10. Accordingly, decentrationsuppression can be three-dimensionally controlled to increase the effectof suppressing decentration.

Furthermore, in this embodiment, since the second water-repellent film25 having higher affinity with the first liquid 41 than with the secondliquid 42 is provided at the center of the hydrophilic film 24, thesecond liquid 42 is repelled by the second water-repellent film 25.Accordingly, a black residue (stain) is eliminated in the opening 50,thus increasing the light transmittance.

Furthermore, in this embodiment, decentration is suppressed by a simplestructure in which the second water-repellent film 25 is provided at thecenter of the hydrophilic film 24. In addition, the electrode in theliquid iris 10 of this embodiment is flat, which is different from theconcave electrode of the optical element (see FIG. 18) disclosed indocument '792. Accordingly, the liquid iris 10 of this embodiment has asimple structure as compared with that disclosed in document '792, andthus the thickness of the liquid iris 10 can be reduced.

[Method of Making Liquid Iris]

Next, a method of making the liquid iris 10 of this embodiment will nowbe described with reference to FIG. 5. FIG. 5 is a flowchart showing aprocedure for making the liquid iris 10.

First, a first substrate 12 composed of a light-transmissive materialsuch as transparent glass is prepared. Next, a first electrode 13composed of a light-transmissive electrically conductive material (e.g.,ITO) is formed on a surface of the first substrate 12 by a vapordeposition method or the like so as to have a film thickness of about 30nm (Step S1). Next, a dielectric film composed of polyvinylidenechloride, polyvinylidene fluoride, or the like and having a thickness inthe range of, for example, about 1 to 5 μm is, for example, bonded ontothe first electrode 13 with an adhesive to form an insulating film 14(Step S2).

Next, a fluorocarbon resin or the like is applied onto the insulatingfilm 14 by a spin-coating method or the like and baked at, for example,150° C. to form a first water-repellent film 15 having a thickness inthe range of about 10 to 30 nm (Step S3). A first substrate portion 11is prepared by Steps S1 to S3 described above.

In addition, a second substrate portion 21 and a sidewall portion 31 areprepared as follows in parallel with Steps S1 to S3. First, a secondsubstrate 22 composed of a light-transmissive material such astransparent glass is prepared. Next, a second electrode 23 composed of alight-transmissive electrically conductive material (e.g., ITO) isformed on a surface of the second substrate 22 by a vapor depositionmethod or the like so as to have a film thickness of about 30 nm (StepS4).

Next, a sidewall member 32 is bonded onto the second electrode 23 using,for example, a UV-curable adhesive (Step S5). Next, a polyvinyl alcoholresin, a polyacrylic acid resin, or the like is applied onto the secondelectrode 23 and the inner wall of the sidewall member 32 by aspin-coating method or the like to form a hydrophilic film 24 and ahydrophilic film 33, respectively, each having a thickness in the rangeof about 300 to 600 nm (Step S6).

Next, a second water-repellent film 25 is formed at the center of thehydrophilic film 24 (Step S7). In this step, the thickness of the secondwater-repellent film 25 is controlled to be substantially the same asthe thickness of the hydrophilic film 24. The second water-repellentfilm 25 can be formed by the following method. First, the hydrophilicfilm 24 is formed on the entire surface of the second electrode 23.Next, an area of the hydrophilic film 24 other than a portion where thesecond water-repellent film 25 is to be formed is masked. Next, theportion of the hydrophilic film 24 where the second water-repellent film25 is to be formed is removed by an etching method or the like. Afluorocarbon resin or the like is then applied onto the portion fromwhich the hydrophilic film 24 has been removed, thus forming the secondwater-repellent film 25. Alternatively, the following method may beemployed. First, a portion of the second electrode 23 where the secondwater-repellent film 25 is to be formed is masked, and a polyvinylalcohol resin, a polyacrylic acid resin, or the like is applied thereonby a spin-coating method or the like to form the hydrophilic film 24.Next, the hydrophilic film 24 is masked, and a fluorocarbon resin or thelike is then applied thereon to form the second water-repellent film 25.

The second substrate portion 21 and the sidewall portion 31, and amember produced by connecting the second substrate portion 21 to thesidewall portion 31 are prepared by Steps S4 to S7 described above.

Next, the first substrate portion 11 and the member produced byconnecting the second substrate portion 21 to the sidewall portion 31,which are prepared as described above, are bonded to each other using,for example, a UV-curable adhesive (Step S8). In this step, the firstsubstrate portion 11 is bonded to the member such that the firstwater-repellent film 15 faces the hydrophilic film 24 (and secondwater-repellent film 25). In this step, an accommodating chamber 40 forenclosing a first liquid 41 and a second liquid 42 is formed in theliquid iris 10.

Next, an antireflection film (not shown) is formed on a desired surface(surface on the light-incident side or the light-emitting side) of theliquid iris 10 by a vapor deposition method or the like (Step S9). Forexample, a multilayered antireflection film in which low-refractiveindex layers and high-refractive index layers are alternately stackedmay be used as the antireflection film. For example, the antireflectionfilm is formed of LaTiO₃/SiO₂ films or the like, and the thicknessthereof is, for example, about 400 nm.

Next, the first liquid 41 and the second liquid 42 are injected into theaccommodating chamber 40 from an inlet 32 a provided through thesidewall member 32 using a syringe or the like (Step S10). In this step,first, a predetermined amount of second liquid 42 is injected into theaccommodating chamber 40, and the first liquid 41 is then filled in theremaining space in the accommodating chamber 40. In this step, the firstliquid 41 and the second liquid 42 are filled so that air does notremain in the accommodating chamber 40. The ratio of the amount of firstliquid 41 injected to the amount of second liquid 42 injected isappropriately adjusted in accordance with the degree of wettability ofthe second liquid 42 on the hydrophilic films 24 and 33, the degree ofwettability of the first liquid 41 on the first water-repellent film 15and the second water-repellent film 25, the diameter of the secondwater-repellent film 25 etc.

Next, the first electrode 13 and the second electrode 23 are connectedto the power supply 8 (Step S11). Lastly, for example, a UV-curableadhesive (adhesive member 34) is applied onto the sidewall member 32,and the adhesive is then cured by ultraviolet irradiation to seal theinlet 32 a of the sidewall member 32 (Step S12). Accordingly, theaccommodating chamber 40 is hermetically sealed to seal the first liquid41 and the second liquid 42 therein. As described above, the liquid iris10 is produced in this embodiment.

[Operation of Liquid Iris]

Before a description of an operation of the liquid iris 10 of thisembodiment when a voltage is applied thereto, an electrowettingphenomenon (electrocapillarity) will be briefly described.

FIGS. 6A and 6B are views showing the principle of the electrowettingphenomenon. FIG. 6A is a view showing a state of a polar liquid 80 whenno voltage is applied to the polar liquid 80, and FIG. 6B is a viewshowing a state of the polar liquid 80 when a voltage is applied to thepolar liquid 80.

In the example shown in FIGS. 6A and 6B, a member includes a substrate81, an electrode 82 disposed on the substrate 81, an insulating film 83disposed on the electrode 82, and a water-repellent film 84 (hydrophobicfilm) disposed on the insulating film 83. It is assumed that a polarliquid 80 (e.g., water) is dropped on the water-repellent film 84. Thepolar liquid 80 is connected to a terminal of a power supply 85 througha switch 86, and another terminal of the power supply 85 is connected tothe electrode 82. In this example, as shown in FIG. 6A, positiveion-molecules 80 a and negative ion-molecules 80 b are present in thepolar liquid 80.

When no voltage is applied to the polar liquid 80 (when the switch 86 isin the off-state), the surface of the polar liquid 80 becomes spherical(the state shown in FIG. 6A) because of the surface tension. In thiscase, the angle formed by the surface of the water-repellent film 84 andthe portion of the liquid surface of the polar liquid 80 that is incontact with the water-repellent film 84, that is, the contact angle isrepresented by θ₀.

When the switch 86 is closed and a voltage is applied to the polarliquid 80, positive charges 83 a are generated on a surface of theinsulating film 83 and negative charges 83 b are generated on anothersurface thereof. In the example shown in FIGS. 6A and 6B, the positivecharges 83 a are generated on the polar liquid 80 side of the insulatingfilm 83, and the negative charges 83 b are generated on the electrode 82side of the insulating film 83. In this case, an electrostatic forceacts on the negative ion-molecules 80 b of the polar liquid 80, and thenegative ion-molecules 80 b are attracted to the water-repellent film 84on the insulating film 83. As a result, the polar liquid 80 adheres tothe water-repellent film 84 in a spread-out manner (the state shown inFIG. 6B), as compared with the case where no voltage is applied (thestate shown in FIG. 6A). The contact angle θ of the polar liquid 80 atthat time becomes smaller than the contact angle θ₀ when no voltage isapplied. Specifically, the wettability of the polar liquid 80 on thewater-repellent film 84 (i.e., affinity between the polar liquid 80 andthe water-repellent film 84) is increased by applying the voltage. Thisphenomenon is referred to as an electrowetting phenomenon.

In this embodiment, the shape of the interface between the first liquid41 and the second liquid 42 enclosed in the liquid iris 10 is changed byutilizing the above-described electrowetting phenomenon to perform theaperture operation of the liquid iris 10.

FIGS. 7A and 7B show the state of the operation of the liquid iris 10when a voltage V₁ is applied between the first electrode 13 and thesecond electrode 23. FIG. 7A is a cross-sectional view of the liquidiris 10 when the voltage V₁ is applied, and FIG. 7B is a top view of theliquid iris 10 viewed from the light-incident side at that time. Whenthe voltage V₁ is applied between the first electrode 13 and the secondelectrode 23, the first liquid 41 is further pressed onto films on thesecond substrate portion 21 side through an electrowetting phenomenon.Consequently, a contact area between the first liquid 41 and the filmson the second substrate portion 21 side, i.e., the diameter of acircular opening 50 formed on the light-incident side of the liquid iris10 increases. For example, in the example shown in FIGS. 7A and 7B, whenthe voltage V₁ is applied, the diameter of the opening 50 becomes T₁,which is larger than the diameter of the opening 50 in the static state(see FIG. 2B).

With reference to FIG. 8, a description will be made of the principlethat when a voltage is applied between the first electrode 13 and thesecond electrode 23, the contact area between the first liquid 41 andthe films on the second substrate portion 21 side increases. FIG. 8 is aview showing the principle of an operation when a voltage is applied tothe liquid iris 10. In FIG. 8, a description will be made of an examplein which positive charges 14 a are generated on the liquid side of theinsulating film 14, and negative charges 14 b are generated on the firstelectrode 13 side of the insulating film 14.

When a voltage is applied between the first electrode 13 and the secondelectrode 23, positive charges 14 a are generated on the liquid side ofthe insulating film 14. In this case, an electrostatic force acts on thenegative ion-molecules 42 b in the second liquid 42, which is a polarliquid, and the negative ion-molecules 42 b are attracted to the firstwater-repellent film 15 side (as shown by the white arrows in FIG. 8).In this case, the second liquid 42 is made to spread over the firstwater-repellent film 15 through the electrowetting phenomenon.Consequently, a pushing force (shown by the black arrows in FIG. 8) actsto the first liquid 41 from the second liquid 42, which is presentaround the first liquid 41. Accordingly, the surface shape of the firstliquid 41 on the hydrophilic film 24 side is changed so as to be pushedtoward the hydrophilic film 24 side (as shown by the hatched arrow inFIG. 8). As a result, a part of the surface of the first liquid 41 onthe hydrophilic film 24 side is pressed onto the films on thehydrophilic film 24 side. As a result, the contact area between thefirst liquid 41 and the films on the second substrate portion 21 sideincreases, thus increasing the diameter of the opening 50 formed on thelight-incident side (hydrophilic film 24 side) of the liquid iris 10.

Furthermore, when the voltage applied between the first electrode 13 andthe second electrode 23 is increased, the second liquid 42 is made tofurther spread over the first water-repellent film 15 through theelectrowetting phenomenon. Accordingly, the pushing force (shown by theblack arrows in FIG. 8) acting from the second liquid 42 to the firstliquid 41 further increases, and the shape of the surface of the firstliquid 41 on the hydrophilic film 24 side is changed so as to be furtherpushed to the hydrophilic film 24 side. Specifically, an angle ofinclination formed between the first water-repellent film 15 and theinterface of the first liquid 41 and the second liquid 42 furtherincreases. In this case, the contact area between the first liquid 41and the films on the hydrophilic film 24 side further increases, therebyfurther increasing the diameter of the opening 50. FIGS. 9A and 9B showthis state.

FIG. 9A is a cross-sectional view of the liquid iris 10 when a voltageV₂ (>V₁) is applied between the first electrode 13 and the secondelectrode 23, and FIG. 9B is a top view of the liquid iris 10 viewedfrom the light-incident side at that time. When the voltage appliedbetween the first electrode 13 and the second electrode 23 is increasedfrom V₁ to V₂, the diameter of the opening 50 formed on thelight-incident side of the liquid iris 10 is also increased from T₁ toT₂.

As described above, in the liquid iris 10 of this embodiment, a part ofthe first liquid 41 is fixed to the second water-repellent film 25provided at the center of the hydrophilic film 24 in the static state.Accordingly, the opening 50 formed during the application of a voltageexpands centering on the second water-repellent film 25. That is, evenduring the application of a voltage, a shift (decentration) of thecenter of the opening 50 formed on the light-incident side from theoptical axis does not occur. Consequently, according to this embodiment,decentration can be suppressed even during the application of a voltage,thus suppressing a decrease in the resolution.

Second Embodiment

In a second embodiment, a description will be made of an example inwhich the structure of the first electrode is changed in the structureof the liquid iris 10 of the first embodiment.

[Structure of Imaging Device]

FIGS. 10A and 10B are schematic views of a liquid iris of thisembodiment. FIG. 10A is a cross-sectional view of a liquid iris 60 whenno voltage is applied. FIG. 10B is a top view of the liquid iris 60viewed from the incident side of a light beam 30 at that time. In theliquid iris 60 shown in FIGS. 10A and 10B, the same components as thoseof the liquid iris 10 (shown in FIGS. 2A and 2B) of the first embodimentare assigned the same reference numerals.

The liquid iris 60 includes a first substrate portion 61, a secondsubstrate portion 21, and a sidewall portion 31 that connects the firstsubstrate portion 61 to the second substrate portion 21. A first liquid41 and a second liquid 42 are hermetically sealed in an accommodatingchamber 40 constituted by the first substrate portion 61, the secondsubstrate portion 21, and the sidewall portion 31.

The structure of the liquid iris 60 of this embodiment is the same asthat of the liquid iris 10 of the first embodiment except that thestructure of a first electrode 63 of the first substrate portion 61 ischanged. Therefore, a description of the structure other than the firstelectrode 63 is omitted here.

FIG. 11 shows a schematic structure of the first electrode 63 used inthis embodiment. An electrode opening 63 b is provided at the center ofan electrode portion 63 a of the first electrode 63. The electrodeportion 63 a of the first electrode 63 is composed of the same materialas the first electrode 13 of the first embodiment and has the samethickness as that of the first electrode 13 thereof. A first substrate12 on which the first electrode 63 is provided is exposed at theelectrode opening 63 b.

The electrode opening 63 b is a star-shaped opening. The electrodeopening 63 b in this embodiment includes a circular portion 63 cdisposed at the center of the first electrode 63 and four projectingportions 63 d. The projecting portions 63 d are separately disposedaround the circumference of the circular portion 63 c at intervals of 90degrees, and each project from the circumference toward the outside inthe shape of an inverted-V character.

The electrode opening 63 b can be formed (patterned) as follows. First,the first electrode 63 is formed over the entire surface of the firstsubstrate 12 as in the first embodiment (Step S1 in FIG. 5). Next, aportion of the first electrode 63 corresponding to the electrode opening63 b is removed by a wet-etching method or the like to form theelectrode opening 63 b. Alternatively, a portion of the first substrate12 corresponding to the electrode opening 63 b is masked, and the firstelectrode 63 may then be formed on the first substrate 12. The liquidiris 60 of this embodiment can be prepared as in the first embodimentexcept that the electrode opening 63 b is formed as described above.

[Principle of Suppressing Decentration]

FIG. 12 is a view showing the principle of suppressing decentration ofan opening when the star-shaped electrode opening 63 b is formed at thecenter of the first electrode 63. When the position of the first liquid41 (insulating transparent liquid) is shifted (decentered) from thecenter of the first electrode 63 on the first electrode 63 as shown inFIG. 12, an area where the first liquid 41 overlaps the electrodeportion 63 a becomes nonuniform (i.e., the symmetry of the area islost).

When a voltage is applied to the liquid iris 60 in such a state, thebalance of the pushing forces acting from the second liquid 42 to thefirst liquid 41 due to an electrowetting phenomenon is disrupted. Inthis case, a force to balance the pushing forces, i.e., a restorationforce (shown by the white arrow in FIG. 12) for returning the firstliquid 41 to the center of the first electrode 63 acts on the firstliquid 41. Accordingly, in this embodiment, the restoration force actsduring application of a voltage so that the first liquid 41 is locatedat the center of the first electrode 63, and thus decentration of theopening can be suppressed. Accordingly, in this embodiment, the effectof suppressing decentration on the first electrode 63 (on the firstwater-repellent film 15) can be further increased.

[Other Examples of First Electrode]

The shape of the electrode opening 63 b of the first electrode 63 is notlimited to the star shape shown in FIG. 11. As for the star shape of theelectrode opening, a plurality of projections projecting from the centerto the outside are arranged in a direction around the center of thefirst electrode at substantially the same distance from each other(substantially the same interval). FIGS. 13 to 17 show examples of anelectrode opening having a star shape other than the shape shown in FIG.11.

In the example shown in FIG. 13, an electrode opening 70 b includes acircular portion 70 c disposed at the center of a first electrode 70 andsix projecting portions 70 d. The projecting portions 70 d areseparately disposed around the circumference of the circular portion 70c at intervals of 60 degrees, and each project from the circumferencetoward the outside in the shape of an inverted-V character.

In the example shown in FIG. 14, an electrode opening 71 b includes acircular portion 71 c disposed at the center of a first electrode 71 andeight projecting portions 71 d. The projecting portions 71 d areseparately disposed around the circumference of the circular portion 71c at intervals of 45 degrees, and each project from the circumferencetoward the outside in the shape of an inverted-V character.

In the example shown in FIG. 15, an electrode opening 72 b includes acircular portion 72 c disposed at the center of a first electrode 72 andsix projecting portions 72 d. The projecting portions 72 d areseparately disposed around the circumference of the circular portion 72c at intervals of 60 degrees, and each project from the circumferencetoward the outside in the shape of an inverted-V character. In thisexample shown in FIG. 15, the leading end of each of the projectingportions 72 d has a circular arc shape concentric with the circularportion 72 c.

In the example shown in FIG. 16, an electrode opening 73 b includes acircular portion 73 c disposed at the center of a first electrode 73 andthree projecting portions 73 d. The projecting portions 73 d areseparately disposed around the circumference of the circular portion 73c at intervals of 120 degrees, and each project from the circumferencetoward the outside in the shape of an inverted-V character.

In the example shown in FIG. 17, an electrode opening 74 b includes acircular portion 74 c disposed at the center of a first electrode 74 andsix rectangular projecting portions 74 d each having a uniform width.The projecting portions 74 d are separately disposed around thecircumference of the circular portion 74 c at intervals of 60 degrees,and each project from the circumference toward the outside.

The electrode opening of the first electrode may have any shape as longas when the first liquid 41 is located at the center of the firstelectrode, an area where the first liquid 41 overlaps the electrodeportion is symmetric with respect to the center of the first electrode.

In the embodiments described above, examples in which a second electrode23 composed of a transparent electrode film is provided on a secondsubstrate 22 have been described, but the present application is notlimited thereto. For example, as in document '792, a rod-shapedelectrode may be used as the second electrode. In such a case, therod-shaped electrode is inserted from the sidewall portion, and an endof the rod-shaped electrode is directly in contact with the secondliquid 42. In such a case, the hydrophilic film 24 and the secondwater-repellent film 25 are formed directly on the second substrate 22.

In the embodiments described above, a description has been made ofexamples in which the present application is applied to a liquid iris,but the present application is not limited thereto. The presentapplication can be applied also to an optical element such as a shutteror a lens. However, when the present application is applied to a lens,both the first liquid 41 and the second liquid 42 are constituted bytransparent liquids, and liquids having refractive indices differentfrom each other are used as the first liquid 41 and the second liquid42.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. An optical element comprising: a first liquid; a second liquid thatis immiscible with the first liquid and that has polarity or electricalconductivity; a first substrate portion including a first substratehaving optical transparency, a first electrode disposed on a surface ofthe first substrate and having optical transparency, an insulating filmdisposed on the first electrode and having optical transparency, and afirst film disposed on the insulating film and having higher affinitywith the first liquid than with the second liquid and opticaltransparency; a second substrate portion including a second substratehaving optical transparency, a second film disposed on a surface of thesecond substrate and having higher affinity with the second liquid thanwith the first liquid and optical transparency, and a third filmdisposed at the center of the second film and having higher affinitywith the first liquid than with the second liquid and opticaltransparency; a sidewall portion connecting the first substrate portionto the second substrate portion so that the first film and the secondfilm face each other; a second electrode disposed on one of the secondsubstrate portion and the sidewall portion; and an accommodating portionconstituted by the first substrate portion, the second substrateportion, and the sidewall portion and sealing the first liquid and thesecond liquid therein.
 2. The optical element according to claim 1,wherein the light transmittance of the first liquid is higher than thelight transmittance of the second liquid, and the refractive index ofthe first liquid is the same as the refractive index of the secondliquid.
 3. The optical element according to claim 1, wherein the surfaceof the third film at the accommodating portion side is circular inshape.
 4. The optical element according to claim 1, wherein thethickness of the second film is the same as the thickness of the thirdfilm.
 5. The optical element according to claim 1, wherein a star-shapedopening is provided at the center of the first electrode.
 6. The opticalelement according to claim 1, wherein the second electrode has opticaltransparency and is disposed between the second substrate and the secondfilm.
 7. The optical element according to claim 1, further comprising: afourth film disposed on a surface of the sidewall portion, the surfacebeing adjacent to the accommodating portion, and having higher affinitywith the second liquid than with the first liquid.
 8. An imaging devicecomprising: an optical element including a first liquid, a second liquidthat is immiscible with the first liquid and that has polarity orelectrical conductivity, a first substrate portion including a firstsubstrate having optical transparency, a first electrode disposed on asurface of the first substrate and having optical transparency, aninsulating film disposed on the first electrode and having opticaltransparency, and a first film disposed on the insulating film andhaving higher affinity with the first liquid than with the second liquidand optical transparency, a second substrate portion including a secondsubstrate having optical transparency, a second film disposed on asurface of the second substrate and having higher affinity with thesecond liquid than with the first liquid and optical transparency, and athird film disposed at the center of the second film and having higheraffinity with the first liquid than with the second liquid and opticaltransparency, a sidewall portion connecting the first substrate portionto the second substrate portion so that the first film and the secondfilm face each other, a second electrode disposed on one of the secondsubstrate portion and the sidewall portion; and an accommodating portionconstituted by the first substrate portion, the second substrateportion, and the sidewall portion and sealing the first liquid and thesecond liquid therein; a power supply unit configured to apply a voltagebetween the first electrode and the second electrode of the opticalelement; a lens unit configured to focus incident light; and an imagingelement on which the light is focused through the optical element andthe lens unit.